To Dig or Not To Dig: An Experiment in No-Till Growing
Winter in the northern hemisphere is often seen as a time to bring out spades or forks and ‘turn over' or ‘break up' the soil. I know quite a few people who actually enjoy doing this, but if you don't, is it really necessary?
I garden on dense clay, undug for a decade or so, its drainage tested to the limit by the recent abundance of rainfall. Crops are looking good though - brussels sprouts, spring cabbage and Treviso chicory all blooming. Leeks are large and parsnips are yielding beautifully. When harvesting them, the undug soil is full of air holes.
However, many gardeners have been taught by respectable bodies such as the Royal Horticultural Society (RHS) that winter digging, to open up the soil, is vital for next year's growth. They read frequent pieces of advice in the gardening media about the need to dig and aerate, and to incorporate manures and compost, instead of simply placing organic matter on top of the soil.
In fact even the RHS has some gardeners who accept that maybe we can still learn more about soil. In March 2007 they asked me to set up an experiment to compare the results of growing vegetables in dug and undug soil.
I publish below the results of the first year's cropping of these four dug and undug beds, in 2007. They all started as weedy pasture and their history is as follows.
Beds 2 and 4 were first dug in March 2007, with compost and manure incorporated underneath a spit of the turf, which was then placed upside down above the organic matter. Beds 1 and 3 were not dug or touched in any way except to place the same amount of organic matter on top of their pasture turf. This consisted of 5cm (2") of well rotted horse manure and then 10cm (4") of green waste compost, which was sufficient to kill grass, buttercups and even dandelions. The same amount of manure and compost in the dug beds meant that all four beds were at least 15cm (6") above soil level, with boards of wood around them and paths measuring 45cm (18") in between.
The soil is a heavy clay loam which comes up in intractable lumps when dug, needing either frost or alternate drying and wetting before a tilth is possible. On the undug beds, sowing and planting is into the compost on top.
I work the beds in two pairs of dug and not dug, growing the same vegetables in each pair. Mostly I raise plants in the greenhouse, enabling rapid establishment of both spring crops and then second crops in late summer. Looking through the table below should give you an idea of the cropping plan. For example, beds 1 and 2 were planted in early April with lettuce, beetroot, onion and chard plants from the greenhouse, allowing time for second crops planted in July and August.
Harvests Dig/No Dig by Charles Dowding, 2007
| BEDS 2 & 1 | |||
| Dug (kg) | Not Dug (kg) | ||
| Lettuce leaves | 5.85 | 6.65 | 18 plants each bed, 3 months picking |
| Beetroot | 3.05 | 3.29 | |
| Chard | 3.82 | 5.09 | |
| Calabrese | 1.12 | .62 | some cabbage root fly damage |
| Onions | 3.54 | 3.45 | bad mildew on all onions lowered yields |
| 1st harvests total | 17.38 | 19.10 | |
BEDS 1 & 2 (Second Harvest) |
|||
| Dug (kg) | Not Dug (kg) | ||
| Leaf radish | .35 | .35 | cabbage root fly damage |
| Lettuce, leaf | 1.89 | 2.70 | |
| Turnip | 3.10 | 2.60 | roots of tennis ball size on average |
| Swedes | 4.77 (4 roots) | .32 (1 root) | gall midge damage on no dig |
| Sugarloaf chicory | 2.62 | 3.87 | |
| 2nd Harvests total | 12.73 | 9.84 | |
| Grand total | 30.12kg | 28.95kg | |
| BEDS 4 & 3 (Planted later than 1 & 2) | |||
| Dug (kg) | Not Dug (kg) | ||
| Lettuce hearts | .28 | .33 | slug damage, eggs from old pasture |
| Dwarf beans | .50 | 1.32 | more slug damage on dug bed |
| Spring onions | 1.25 | 1.31 | |
| Show onions | 3.67 | 3.43 | 5 onions both beds, some mildew |
| Carrots | 3.10 | 7.98 | less slug damage to seedlings, undug beds |
| Red cabbage | 3.55 | 2.93 | |
| Celeriac | 2.24 | 3.73 | |
| Leeks | 1.36 | 1.51 | leeks were longer on undug bed |
| Mustards | .98 | .93 | |
| Chicories | 1.62 | 2.16 | |
| Grand total | 18.55kg | 25.63kg | |
Totals of the Four Beds |
|||
| Two dug beds | 48.67kg | ||
| Two undug beds | 54.58kg | ||
| NOTE that weights recorded are of vegetables’ main edible parts only - cabbage outer leaves were discarded, onions and celeriac were trimmed, beetroot leaves were removed and so forth. | |||
Characteristics of growth differences
The undug beds showed quicker growth in spring for almost all crops, while the dug beds caught up in summer and autumn for most crops. Salad leaves were nearly all more productive and suffering a little less slug damaged on the undug beds, while the brassicas tended to do better on dug beds.
It will be interesting to set these results against those of 2008, which I shall report in a following article. Meanwhile I wish you a happy festive season with, I hope, plenty of delicious vegetables.
More information at www.charlesdowding.com
